Pulse column with piston drive and resilient gas cushion

ABSTRACT

For controlling the amplitude of pulsations of liquid in a column partly filled with the liquid and having a pulsing chamber which communicates with a gas cushion alternately compressed and expanded at a constant amplitude and frequency comprising: increasing and decreasing the amount of gas in the gas cushion. In the installation according to the invention the space behind the piston in the cylinder is connected with a buffer space, the volume of which is at least as large as that of the gas cushion, while the spaces in front of and behind the piston in the cylinder are connected by means providing a restricted communication.

United gtates Patent 11 1 Van Koppen 1 Mar. 27, 1973 1541 PULSE COLUMNWITH PISTON DRIVE 3,092,515 6/1963 Pike .25 267 c AND RESILIENT GASCUSHION 3,298,79l l/l967 Meyer ..23/267 c 2,767,068 10/1956 Mayeods..23/267 C lnvemorl Cnstlanus Van Koppen 2,852,349 9/1958 Hicks tard,Netherl n 1,509,686 9/1924 Morterud ..23/267 0 3 A' :St b N. V. Herl, [71 sslgnee amlcar on 6 en Primary Examiner-Norman Yudkoff NetherlandsAssistant Examiner-S. J. Emery [22] Filed: F 2 9 Attorney-Cushman, Darby& Cushman 21 A l.No.: 118 344 l 1 pp 57 ABSTRACT For controllin the amlitude of ulsations of li uid in 30 F A 1 tnPront 0m g P P orelgn pplcalo l y a a column partly filled with the liquid and having a Mar. 5,Netherlands l9 pulsing chamber communicates a gas I cushion alternatelycompressed and expanded at a U-S- C, constant amplitude and frequencycomprising; in. s creasing and decreasing the amount of gas in the gasFleld of Search -23/267 310, 309 cushion. In the installation accordingto the invention the space behind the piston in the cylinder is con-References cued nected with a buffer space, the volume of which is atleast as large as that of the gas cushion, while the UNxTED STATESPATENTS spaces in front of and behind the piston in the cylinder2,818,324 12/1957 Thornton ..23/267 C are connected by means providing arestricted com- 2,8ll,423 10/1957 Bradley ..23/267 C munication,2,629,654 2/1953 Olney .....23/267 C 2,090,496 8/1937 Wynn ..23/267 C 9Claims, 2 Drawing Figures PULSE COLUMN WITH PISTON DRIVE AND RESILIEN'IGAS CUSHION 7 BACKGROUND AND SUMMARY OF THE INVENTION of the column anddevices have been installed to utilize lo a pulsed pneumatic pressure ata gas cushion over the liquid surface in the tube, consisting of acylinder and a motor-driven piston. Such a pulse installation has beenproposed by Thornton in U.S. Pat. No. 2,818,324, and has the advantagesthat corrosive column-liquids are not in contact with the pulseinstallation and that the cavitation problem (occurring when pulsing istoo fast, particularly in the case of volatile, organic liquids) isavoided. Because of the compressibility of the gas, however, a largerpulsing capacity is required to obtain a similar result.

The invention aims at meeting this drawback and providing a pulseinstallation with piston drive and resilient gas cushion, such as isdisclosed in the aforementioned United States patent, but in which therequired amount of power is reduced.

In the installation according to the invention the space behind thepiston in the cylinder is connected with a buffer space, the volume ofwhich is at least as large as that of the gas cushion, while the spacesin front of and behind the piston in the cylinder are connected by meansof a narrow connecting line. In most cases the size of the piston can beselected to be undersize, relative to the size of the cylinder so thatthe air crevice between the piston rings and the cylinder wall can serveas the connecting line mentioned.

Another purpose of the invention is to provide a pulse installation ofthe type in question, in which control of the pulsing amplitude iseffected in a simple manner.

With the device of Thornton, the maximum displacement of the liquidaccording to FIG. 2 of his U.S. Pat. No. 2,818,324 automatically adjuststo the frequency set. However, according to Thornton the two variables,

displacement and frequency, can be made independent by constructing apulse installation so large that the desired amplitude occurs at thehighest operating frequency desired and by controlling the amplitude atlowerfrequencies by reducing the stroke of the piston. To this end, withThornton, the motor is constructed as lineair air-motor, while both thespeed and the stroke of this motor are adjustable.

In operating the installation according to the invention, on the otherhand, control of the desired pulsing amplitude is obtained by varyingthe quantity of gas in the gas cushion, while keeping the frequency aswell as the stroke of the piston constant. This method has the advantagethat the driving mechanism need not be constructed as a variable one andcan, therefore, be of optimum efficiency. In addition, the mechanismwill be sturdier and cheaper.

Other advantages and features of the invention will be explained on thebasis of an example of the construction shown in the attached drawing.The principles of the invention will be further hereinafter discussedwith reference to the drawing wherein a preferred embodiment is shown.The specifics illustrated in the drawing are intended to exemplify,rather than limit, aspects of the invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagra'mmatical, verticalcross-section of a pulse column provided with an installation accordingto theinvention.

FIG. 2 is a graph of the relation between the pulsing amplitude (a) andthe average volume (V,) of the gas cushion.

In FIG. 1-, 1 represents a pulse column, which, over part of its length,is provided with a filling 2. Above and below -the-part containing thefilling there are the collecting spaces 3 and 4, which are equipped withliquidconnections 5 and 6, and 7 and 8, respectively. Near the bottomend of the column there is a connection 9 connecting the pulse column 1with a pulsing chamber 10. The chamber 10 is only partially filled withliquid and above the liquid surface there is a gas cushion 12. A tube 13connects the gas cushion with a cylinder 14. In the cylinder 14, apiston 15 can be moved upwards and downwards with the aid of acrank-connecting rod mechanism 16, or a similar mechanism, and a motor17. Therefore, the sum of the volumes of I2, 13 and cylinder 14 abovethe piston 15, with the piston 15 in mid-position, is to be consideredas the average volume (V,,) of the gas cushion.

The space B behind the piston 15 in the cylinder 14 is connected witha'buffer space 18 which has a volume which is at least as large as thatof the gas cushion 12. This buffer space 18 may, if necessary, form awhole with, or be an extension of, said space B in cylinder 14. Thespace A in front of the piston 15 in the cylinder 14 is connected withthe space B behind the piston via a narrow connecting line 19. In manycases the air crevice between the piston and the cylinder wall can serveas connecting line. A supply line 22 for gas emanating from a source notindicated in detail is preferably connected to the buffer space 18,which line can be closed by means of a valve 20. Preferably at the topof the chamber 10, a discharge line 23 is installed,

which can be closed by means ofa valve 21.

FIG. 2 is agraph which at a certain frictional resistance coefficient (i15) of the column filling, renders the stroke (a) of the liquid motionin the column as a function of the average volume (V,,) of the gascushion, the stroke volume and the number of strokes per time unit ofthe piston 15 being considered constant.

The graph is for a pulsed packed column having a height of about 8meters and an inner diameter of about 0.75 meters. The column fillingwas about 6 meters high, and consisted of ceramic Raschig rings of 25 mmouter diameter. The column liquors were various liquids, having aspecific weight not very different from I, and a dynamic viscosity below5 cP (centipoises). The particular gas used in the gas cushion wasnitrogen (N,). displacement of the piston was about 3 liters. The volumeof the gas cushion (including the space A) could be varied from 13 to 40liters and the stroke (a) varied then between 1,5 and 0,4 centimeters.

The extraction efficiency of the system may, in the case of a chosenstroke frequency, depend on the stroke (a) of the liquid pulsations. Inthe installation according to FIG. 1, the stroke (a) depends on the gasvolume V in the manner indicated in FIG. 2. By preference, processingwill take place in the descending part of the curve. This will not onlyyield a larger range of control, but also be simpler from a constructionpoint of view because of the pertaining, larger gas volume. For thestroke to be enlarged or reduced, the gas volume V will be reduced orenlarged with the aid of the two valves 20 and 21. The pressureamplitude in chamber has shown to be substantially proportional to thepulsing amplitude a; these pressure fluctuations, therefore, can serveas a measure of the pulsing am plitude a.

By the provision of the buffer space 18, the pressure variations behindthe piston are kept smaller than, for instance, 0.1 atm, while thepiston is relieved in its upward and downward motion, which is not onlyfavorable in relation to energy, but also reduces the frictional lossesin the driving mechanism 16. Starting up is easier, too, and further,the stresses occurring in the driving mechanism 16 are smaller.

The quantity of'gas present in the gas cushion 12 can be kept constantvia the supply line 22 with the aid of automatically operating devicesknown by themselves, which are not shown in the figures, for anunintentional gas loss would cause the amplitude of the pulsations inthe column to become greater. The only point where loss of gas willinevitably occur is from the stuffing box 24 where the piston rod ispassed through the cylinder cover. Notably, if nitrogen is applied, asis the case with such inflammable column liquids as benzene, thisstuffing box should be of good quality. In addition, by continuouslypurging gas via line 22, space 18, space B, line 19, space A, line 13and space 12 to the discharge line 23, it is also achieved that anydroplets or vapors of the column liquid accumulating in the chamber 10are discharged.

The diameter of the pulsing chamber 10 is so wide that during thepulsations, the accelerations occurring always remain smaller than theacceleration of the gravity g. The advantage of this is that dropformation at the liquid surface does not occur. (As in the case ofThornton, formation of vapor bubbles in the column liquid, the so-calledcavitation, cannot occur either.)

In the pulsing chamber 10 a vertically arranged wave damper 11consisting of a perforated plate or something similar can be providedboth to avoid excessive wave motions and to prevent the liquid frombeing flung up at the liquid surface.

In those cases that vapor might condense in the cylinder 14, it isadvisable for the cylinder 14 to be placed higher than the connectingline 13 and the liquid surface in the pulsing chamber 10.

In the pulsing chamber 10, a float valve (not shown) can be installed(in a manner as is known, for instance, from FIG. 4 of the British Pat.Specification No. 780,406) to avoid the influx of column liquid into theline 13.

it should now be apparent that the process and apparatus for pulsating aliquid in a pulsating column as described hereinabove possesses each ofthe attributes set forth in the specification under the headingBackground and Summary of the invention hereinbefore. Because theprocess and apparatus for pulsating a liquid in a pulsating column ofthe invention can be modified to some extent without departing from theprinciples of the invention as they have been outlined and explained inthis specification, the present invention should be understood asencompassing all such modifications as are within the spirit and scopeof the following claims.

What is claimed is:

1. As an improvement for a combination which includes:

an extraction column partly filled with liquid to be pulsed and withfilling means for enhancing extraction; a U-shaped pulsing chamberexternal of the column having a connection with the lower end of thecolumn with means defining a gas cushion above the liquid surface in thechamber; a piston slidably received in a sealed cylinder external ofsaid pulsing chamber and communicating with the gas cushion; and meansfor oscillating the piston in the cylinder to increase and decrease theforcewith which the gas cushion acts upon the liquid surface in thechamber in order to cause the liquid in the column and the chamber topulsate;

means defining a sealed buffer chamber external of said pulsing chamberand having a volume at least as large as the average volume of the gascushion, said buffer chamber being communicated to said cylinder on theopposite side of said piston from said gas cushion; and means providingrestricted communication between the cylinder on the same side of saidpiston as the gas cushion and on the same side of said piston as thebuffer chamber.

2. The apparatus of claim 1 wherein the pulsing chamber is of such greatcross-sectional area that during the pulsations, the acceleration ofliquid at the liquid surface due to pulsation is always less than theacceleration due to gravity.

3. The apparatus of claim 2 further including perforated plate meanswithin the pulsing chamber for retarding wave motion at the liquidsurface.

4. The apparatus of claim 1 wherein said means for oscillating thepiston comprises a motor.

5. The apparatus of claim 4 wherein said motor is connected to thepiston by means providing a constant amplitude and frequency of pistontravel.

6. The apparatus of claim 1 further including means for continuouslyadmitting gas to said buffer chamber and means for continuouslydischarging gas from the gas cushion for purging the gas cushion ofliquid.

7. The apparatus of claim 1 wherein the increase and decrease inpressure within the cylinder on the opposite side of the piston from thegas cushion during pulsations has a magnitude of less than 0.1atmosphere.

8. The apparatus of claim 1 further including means for increasing anddecreasing the amount of gas within the system comprising the gascushion, the buffer chamber and the restricted communication for varyingthe amplitude of pulsations in the column.

9. As an improvement for a combination which includes:

an extraction column partly filled with liquid to be pulsed and withfilling means for enhancing extraction; a U-shaped chamber external ofthe column having a connection with the lower end of the column withmeans defining a gas cushion above the liquid surface in the chamber; apiston slidably received in a sealed 'cylinder external of said 6pulsing chamber and communicating with the gas pulsing chamber having avolume at least as large cushion; and means for oscillating the pistonin the as the average volume f the gas Cushion Said cylinder to increaseand decrease the force with buffer chamber being communicated to saidwhich the gas cushion acts upon the liquid surface in the chamber inorder to cause the liquid in the 5 column and the chamber to pulsate;means defining a sealed buffer chamber external of said cylinder on theopposite side of said piston from said gas cushion.

2. The apparatus of claim 1 wherein the pulsing chamber is of such greatcross-sectional area that during the pulsations, the acceleration ofliquid at the liquid surface due to pulsation is always less than theacceleration due to gravity.
 3. The apparatus of claim 2 furtherincluding perforated plate means within the pulsing chamber forretarding wave motion at the liquid surface.
 4. The apparatus of claim 1wherein said means for oscillating the piston comprises a motor.
 5. Theapparatus of claim 4 wherein said motor is connected to the piston bymeans providing a constant amplitude and frequency of piston travel. 6.The apparatus of claim 1 further including means for continuouslyadmitting gas to said buffer chamber and means for continuouslydischarging gas from the gas cushion for purging the gas cushion ofliquid.
 7. The apparatus of claim 1 wherein the increase and decrease inpressure within the cylinder on the opposite side of the piston from thegas cushion during pulsations has a magnitude of less than 0.1atmosphere.
 8. The apparatus of claim 1 further including means forincreasing and decreasing the amount of gas within the system comprisingthe gas cushion, the buffer chamber and the restricted communication forvarying the amplitude of pulsations in the column.
 9. As an improvementfor a combination which includes: an extraction column partly filledwith liquid to be pulsed and with filling means for enhancingextraction; a U-shaped chamber external of the column having aconnection with the lower end of the column with means defining a gascushion above the liquid surface in the chamber; a piston slidablyreceived in a sealed cylinder external of said pulsing chamber andcommunicating with the gas cushion; and means for oscillating the pistonin the cylinder to increase and decrease the force with which the gascushion acts upon the liquid surface in the chamber in order to causethe liquid in the column and the chamber to pulsate; means defining asealed buffer chamber external of said pulsing chamber having a volumeat least as large as the average volume of the gas cushion, said bufferchamber being communicated to said cylinder on the opposite side of saidpiston from said gas cushion.